In order to use Windows native SSL support define 'USE_WINSSL'

This option may be used to build curl/libcurl using SSL/TLS support provided
by MS windows system libraries. Option is mutually exclusive with any other
SSL library. Default value is --without-winssl.

--with-winssl option implies --with-sspi option.

Option meaningful only for Windows builds.

This is more descriptive for the user who might
not even know what schannnel is at all.

Version number is removed in order to make this info consistent with
how we do it with other MS and Linux system libraries for which we don't
provide this info.

Identifier changed from 'WinSSPI' to 'schannel' given that this is the
actual provider of the SSL/TLS support. libcurl can still be built with
SSPI and without SCHANNEL support.

No need to check if 'entry' is non-NULL in a spot where it is already checked
and guaranteed to be non-NULL.

(Spotted by a Coverity scan)

Remove two states from the enum and the corresponding code for them as
these states were never reached or used.

(Spotted by a Coverity scan)

This reverts commit 9c94236e.

It didn't server its purpose, so lets go back to long-time working code.

Removed obsolete minor status variable and parameter of status function
which was never used or set at all. Also Curl_sspi_strerror does support
only one status and there is no need for a second sub status.

Make sure CURL_VERSION_SSPI is present and works as in previous releases
for ABI and API compatibility reasons.

Removed specific WITH_SSL=schannel paramter that did not fit the general
schema and complicated the parameters. For now Schannel will be enabled
if SSPI is enabled and OpenSSL is disabled.

Added Windows SSPI version information to the curl version string when
SCHANNEL SSL is not enabled, as the version of the library should also
be included when SSPI is used to generate security contexts.

Removed SSPI from the feature list as the features are GSS-Negotiate,
NTLM and SSL depending on the usage of the SSPI library.

Removed duplicate blank lines.
Removed spaces between the not and test in various if statements.
Removed explicit test of NULL in an if statement.
Placed function returns on same line as function declarations.
Replaced the use of curl_maprintf() with aprintf() as it is the
preprocessor job to do this substitution if ENABLE_CURLX_PRINTF
is set.

Reworked the version function to return four version components rather
than a string that has to be freed by the caller.

curl_sspi.c: Fixed mingw32-gcc compiler warnings
curl_sspi.c: Fixed length of error code hex output

The hex value was printed as signed 64-bit value on 64-bit systems:
SEC_E_WRONG_PRINCIPAL (0xFFFFFFFF80090322)

It is now correctly printed as the following:
SEC_E_WRONG_PRINCIPAL (0x80090322)

curl_sspi.c: Fallback to security function table version number
Instead of reporting an unknown version, the interface version is used.

curl_sspi.c: Removed SSPI/ version prefix from Curl_sspi_version
curl_schannel: Replaced static buffer sizes with defined names
curl_schannel.c: First brace when declaring functions on column 0
curl_schannel.c: Put the pointer sign directly at variable name
curl_schannel.c: Use structs directly instead of typedef'ed structs
curl_schannel.c: Removed space before opening brace
curl_schannel.c: Fixed lines being longer than 80 chars

Added new function to get SSPI version as string.
Added required library version.lib to makefiles.
Changed curl_schannel.c to use Curl_sspi_version.

Moved type definitions in order to avoid inclusion loop

Moved the error constant switch to curl_sspi.c and added two new helper
functions to curl_sspi.[ch] which either return the constant or a fully
translated message representing the SSPI security status.
Updated socks_sspi.c and curl_schannel.c to use the new functions.

Windows 2000 Professional:  Schannel returns SEC_E_OK instead
of SEC_I_CONTEXT_EXPIRED. If the length of the output buffer
is zero and the first byte of the encrypted packet is 0x15,
the application can safely assume that the message was a
close_notify message and change the return value to
SEC_I_CONTEXT_EXPIRED.

Connection shutdown does not mean that there is no data to read
Correctly handle incomplete message and ask curl to re-read
Fixed buffer for decrypted being to small
Re-structured read condition to be more effective
Removed obsolete verbose messages
Changed memory reduction method to keep a minimum buffer of size 4096

Updated TODO information and added related MSDN articles